The present invention relates to the field of surgical instruments, and more particularly to the field of instruments for use in spinal fusion procedures. More particularly still, the present invention relates to an extraction instrument for use in harvesting an iliac bone graft, and an insertion instrument for use in placing the graft in a spinal disc space. The instruments of the present invention have particular utility in the course of performing anterior cervical fusion procedures according to a modified Robinson technique, but may also be used in other types of procedures, for example, lumbar interbody fusions.
The human spine, vertebral column, or backbone comprises a plurality of stacked vertebrae, each vertebra consisting of a ventral body, or centrum, surmounted by a Y-shaped neural arch. Together the centrum and neural arch surround an opening, the vertebral foramen, through which the spinal cord passes. The centrums are separated by cartilaginous intervertebral discs, which help to cushion shocks to which the vertebral column is subjected. The human spine comprises seven (7) cervical or neck vertebrae, twelve (12) thoracic, five (5) lumbar, and fused sacral and caudal vertebrae.
From time to time, people may suffer from one of various diseases which affect the intervertebral discs. The discs may become inflamed, swollen, or misshapen, they may break down or deteriorate, or they may even "slip" or protrude partially out of their intervertebral housings, or disc spaces. Sometimes such disease processes are precipitated by an injury or the like. When this happens, the affected disc or discs can exert undue pressure on the spinal cord or spinal nerves extending from it, which can cause extreme pain or discomfort, restrict movement, or even disable the unfortunate victim. Sometimes the affected disc or discs cannot be effectively treated or rehabilitated, and in such cases complete removal of the disc(s) is required.
Removal of diseased or otherwise hopelessly impaired discs may be accompanied by fusion of the adjoining vertebrae with a bone graft taken from elsewhere in the body. In a fusion procedure, the bone graft is inserted in the disc space in place of the removed disc, and the vertebrae above and below the graft grow together with, or become "fused" to, the graft. The resulting fused joint is no longer freely flexible, but the pain is eliminated, the patient will still have some movement around the joint, and he can resume most of his normal life's activities.
When the cervical discs are affected, the fusion procedure is typically accomplished from the front, or anterior, of the neck. This procedure is known to those skilled in the art as an anterior cervical fusion, or an anterior interbody cervical fusion. Several different techniques have been developed for effecting an anterior cervical fusion. According to one such technique, a cylindrical or dowel-shaped graft is inserted into a matching cylindrical space which comprises the disc space and an arcuate portion on the upper and lower sides, or the roof and floor, of the disc space. This is known as a Cloward fusion. Specialized instruments have been developed for use in the Cloward procedure, for assisting in the graft harvesting and insertion steps. Such instruments have been designed, of course, to accommodate the harvesting of a round graft and the handling of that round graft in the insertion phase. Due to drawbacks in the Cloward technique, however, it has been diminishing in popularity of late. One major drawback of the Cloward fusion is that the vertebrae which bound the disc space are weakened due to the arcuate portion removed from them. This is undesirable because the weakened vertebrae are more susceptible to additional injury or damage. This weakening of the vertebrae also makes the Cloward procedure undesirable for fusing two adjacent discs, because the middle vertebra of the three affected vertebrae would have an arcuate portion removed from both its upper and lower faces.
Another prior art technique for performing cervical fusions is the Bailey-Badgley procedure. In a Bailey-Badgley fusion, the graft is shaped somewhat like a tall wedge with a rounded nose, and as is the case with the Cloward technique, the matching space comprises not only the disc space, but also some space from the roof and floor of the disc space. In the Bailey-Badgley procedure, the portions removed from the roof and floor of the disc space are not arcuate, but flat. The Bailey-Badgley fusion suffers from the same major drawbacks as the Cloward technique, in that the vertebrae which bound the disc space are weakened due to the portion removed from them. Thus, the Bailey-Badgley procedure is also undesirable for fusing two adjacent discs.
The most popular cervical fusion technique of late is that of Robinson. In the Robinson technique, an iliac bone graft is inserted into the disc space, with little or no removal of surrounding tissue to accommodate the graft, contrary to both the Cloward and Bailey-Badgley fusions referred to above. The Robinson technique thus can be used effectively to fuse two adjacent discs. In the Robinson fusion, the iliac bone graft is harvested from the edge of the ilium so that cortical bone is present on three sides of the graft. The iliac bone graft is sized and shaped according to the size and shape of the intended disc space, and inserted into the disc space with the middle cortical edge to the anterior. That results in the graft having cortical bone on all three exposed sides. In a modified form of the Robinson technique, the middle cortical edge is inserted into the disc space first, that is, in a posterior position. This tends to help the surgeon with the graft insertion step, because the leading cortical edge is relatively stiff and curved or "bullet shaped," which assists in slipping the graft past the surrounding tissue at the entrance to the intended disc space.
Although the Robinson and modified Robinson techniques have enjoyed much success of late, there are several major drawbacks with the instruments commonly used in performing these procedures which detract from this success. In the graft harvesting phase, quite often the surgeon will use a single-bladed instrument somewhat like a chisel to make a pair of incisions in the ilium to bound the graft. The blades of such chisel-like instruments may have a dual-tapered edge. One drawback with the single-bladed instrument is a lack of positive control on the size and shape of the graft. The surgeon may inadvertently make the graft too small or too large, by making the incisions too close together or too far apart. In the former event the graft may be unusable, and in the latter event the graft will require excess tooling or reshaping. In addition, while the surgeon may wish to have a graft with substantially parallel upper and lower faces, he may inadvertently fail to make the pair of cuts parallel to one another. This also requires excess tooling or reshaping.
One alternative to the single-bladed harvesting instrument discussed above is a small power saw with two parallel oscillating blades. Although this device gives more control over the size and shape of the graft than the single-bladed instrument, a drawback of the device is that small particles of bone are thrown off around the harvesting site or into the air, which may contaminate the physical surroundings and/or medical personnel in the vicinity. With the increasing incidence of disastrous afflictions such as AIDS, the undesirability of such contamination is clear.
With regard to the insertion phase of the Robinson or modified Robinson procedures, typically the graft will be held with a clamp, forceps, or some other such device to place it into the entry of the disc space. Then the graft will usually be engaged by a rod or punch, the end of which is tapped by a mallet, which drives the graft into the disc space. This technique is undesirable, however, because the rod or punch can slip off the disc, possibly injuring the patient. Moreover, the surgeon has less than full control over the orientation of the graft as it is driven into the space; the graft can rotate in the space, causing undue complications to the procedure. In addition, at times the graft may be driven too far into the posterior portion of the disc space. If the graft is driven too far into the region of the spinal cord or other nerves, serious injury to the patient could occur.
An instrument known as a dowel holder has been used in the past for placing the graft in the disc space and holding it during the insertion step, as an alternative to the clamps, forceps, and rod or punch referred to above. A dowel holder typically includes a rectangular head with distally extending pointed supports at its corners, and a distally extending threaded screw shaft in its center. This instrument is used particularly in the Robinson procedure. A hole is drilled in the middle of the central cortical edge of the graft, and the threaded shaft is screwed into the hole. The dowel holder may then be manipulated with the graft screwed to it, to enable the graft to be placed in the entry of the disc space. The end of the dowel holder is then tapped, to drive the graft into place. The pointed corners help keep the graft from rotating while being driven into place. A major drawback with this instrument is that the graft is weakened by drilling the hole in it. The graft may split while being driven into place, which of course seriously complicates the procedure. In addition, there is no positive stop on this instrument which prevents the graft from being driven too far into the disc space, leaving the possibility of causing severe injury to the patient if this were to occur.